Organs are made up of networks of specialized tube types that have distinct sizes, shapes and functions, with the tiniest (unicellular) tubes being just one cell in diameter. Defects in tube development or maintenance underlie many serious health problems such as kidney disease, heart disease and stroke, so it is important to understand factors that shape and maintain tubes. Despite the fact that unicellular tubes are widespread in the capillary beds that interface with other tissues such as the brain and kidney, very little is known about how unicellular tubes develop or are maintained. To address these issues, we study a set of unicellular tubes in the excretory (renal-like) system of the nematode C. elegant. We identified >100 mutants that affect these unicellular tubes, and we will use them to address three main questions. Aim 1) How do Ras signaling and the fusogen AFF-1 promote an elongated tube shape? Many unicellular tubes are seamless -they lack junctions along their length - and they adopt elongated or branched shapes. We will test the hypothesis that aff-1 is a key downstream target of Ras signaling for both seamlessness and tube shape control and has a continuous function in a novel pathway for apical membrane addition. Aim 2) How does the luminal extracellular matrix protect tube integrity? As tubes develop, they secrete various glycoproteins into their lumens. We will test the hypothesis that the Zona Pellucida (ZP) domain protein LET-653 interacts with other gene products we identified to form a luminal matrix scaffold that shapes and protects the lumen during tube morphogenesis, and that unicellular tubes are particularly reliant on such luminal scaffolds for their integrity. Aim 3) How does Ras signaling promote tube delamination? Some cells within an epithelium can delaminate and give rise to other cell types, and this process is co-opted during tumor cell metastasis. We identified a cell non-autonomous requirement for Ras signaling in delamination. We will test the hypothesis that Ras acts in a common pathway with other genes we've identified that are also required for delamination. Our experiments take advantage of powerful imaging and genetic approaches possible in C. elegant to address central questions about unicellular tubes that are also relevant to the biology of all tubes.